The primary orientation of our laboratory for the past ten years of support on this NIH grant has been the determination of the primary structure of immunoglobulin variable regions especially heavy chain variable regions and the relationships of these structures to the antibody combining site and the idiotypic determinants. To this end, our laboratory was initially engaged in the amino acid sequence analysis of randomly chosen human myeloma proteins without known antibody activity. Through these studies heavy chain hypervariable regions were uncovered. By the sequence analysis of two humaa heavy chains which shared idiotypic determinants and with similar antigen-binding specificities, a remarkable amino acid sequence identity in the hypervariable regions of proteins so chosen established that hypervariable regions and the idiotypic determinants were intimately associated. More recently we have been utilizing the arsonate system in A/J mice as a means of approaching similar problems but in a defined inbred strain. The present proposal is directed toward further analysis of variable regions of immunoglobulin polypeptide chains with particular emphasis on heavy chain V regions. Antibodies of defined idiotypic specificity will be selected and their amino acid sequences determined. Special consideration will be given to determining the total variable domain structures of molecules which arise in single mice and for which precise information concerning the idiotype as well as the combining specificity is available. These structures will be compared to molecules arising in the same strain which either through selection or through suppression do not bear the idiotype. In addition, mice from strains which do not carry the same idiotype will be studied. Finally, hybridomas will be generated, their precise specificity and idiotype studied and where appropriate amino acid sequence analysis will be undertaken.